A conventional brake of a bicycle functions as the rider clutches a brake, the brake lever then draws a pair of brake blocks via brake cable to press both sides of the rim of a wheel, a frictional force thus caused may stop rotation of the rim forcibly. As riding a bicycle would consume a lot of energy of the rider, the bicycle must be lighter in weight to save the rider's stamina. To achieve this object, a bicycle must be constructed by simple components and the same applies to the design of the brake mechanism. Though the speed of a bicycle is lower than that of a motorbike, it may still build up considerable speed when riding at a dash, thus it still needs great brake power to secure the safety of a rider.
Thus, the brake mechanism should be designed in order to obtain higher braking force with a limited gripping force. A conventional brake system achieves the effect by using the principle of leverage for which the push arm is longer than a pull arm. It has one other advantage, that is, it provides a sensitive touch of a brake system, but on the other hand, this design tends to lock a rim upon an emergency brake, i.e., the rim ceases rotating instantaneously, and may cause the bicycle to turn over. Further, the rim may be distorted and deformed seriously by the sudden and strong braking force, thus significantly reduce the safety of the rider.